Basis Debut Mk.V turntable
By Michael Fremer   •   January, 2000 As it did for so many other designers and manufacturers of specialty audio gear, the current occupation of Basis owner/designer A.J. Conti began as a hobby and personal quest. A longtime audiophile and home-based dealer of brands like Krell and Quicksilver, Conti decided to build his own "killer" turntable using a fluid-damped suspension.

Armed with a background in mechanical engineering studies at both RPI and Northeastern, and work experience that included high-energy laser and aerospace (missile and helicopter) R&D, Conti set about designing his dream 'table. Once he was ready to build it, he figured he'd make a few extra for friends. Krell's Dan D'Agostino heard the finished product and immediately bought one. Within a few weeks, the first run was spoken for, and Conti found himself with orders for 50 more. That was more than a decade ago; the rest, as they say, is history.

Over the past few years Conti has introduced the physically smaller, less expensive, and thus far more popular 2000 series of turntables, as well as the entry-level 1400. But the $8200 Debut Mk.V ($10,600 with vacuum platter) is the most recent updating of Conti's original design.

The Debut consists of two main components: a 1"-thick cast acrylic base incorporating the four suspension towers of solid, aircraft-grade aluminum, and a 2"-thick cast acrylic main chassis that supports the bearing, the platter, and the interchangeable armboard. The main chassis is suspended from the four towers by thick, semi-sealed, silicone-damped spring cartridges ingeniously designed by Conti.

To suspend the main chassis, you insert the cartridges one at a time through the tower bottoms, which you expose by carefully hanging one foot/tower at a time over the edge of your stand. Then, using a special threaded T tool, you pull the spring cartridge up into the tower until the holes drilled in it line up with openings in the tower. Insert two tiny steel pins and you're done. Pulling up the spring with one hand while inserting the pins with the other is a bit tricky, but I managed to install all four suspensions without dropping a pin. (Basis supplies extras in case you accidentally drop one into the tower. If you do, it won't come out, but it won't affect performance either.) When you're finished, you fit four threaded feet into the bottom of the towers; then, using a spirit level, you level the base.

Once you've mounted the 19-lb platter and the 9-lb armboard, the effectiveness of the hanging-suspension system becomes apparent. The Debut's suspension is a true low-frequency (3–4Hz) isolation system that works both horizontally and vertically, and behaves much like far more complicated and costly air-suspension systems.

19-lb platter
But back to that 19-lb, 2"-thick platter: it's solid acrylic, with brass inserts of various diameters that add mass and break up resonances. The Debut Mk.V's platter is balanced at high speed on the same machine used to balance racing crankshafts. There is also an aluminum insert placed around the 1⁵/₈"-diameter center hole that accepts the bearing assembly and through which the spindle protrudes from the top of the platter.

When the platter is riding on its matched bearing, the claimed eccentricity spec is ±0.0005"—which A.J. Conti confirmed for me with a dial gauge applied to the outside of the platter. A heavy, very effective record clamp, machined of aluminum and fitted with a locking collet, is available for $250.

The bearing/sleeve itself is a fairly standard ball-bearing/oil-well design fitted with a pair of bushings. What is somewhat unusual (and desirable) is the system's low center of gravity, achieved by hollowing out the platter's center so the bearing goes way up inside—about ³/₈" below the record-playing surface. The result is a design that uses a heavy platter while maintaining very low horizontal bushing force.

Some designers achieve the same low center of gravity more easily by inverting the bearing, with the well pointing downward. However, this places the point of contact—a potential source of noise—closer to the record-playing surface, and forces the system to be run dry.

All critical surfaces of the bearing shaft are ground using the same tool in a single sequence. This ensures that the center spindle, the bearing bushings, and the hole at the bottom for the tungsten-carbide ball are all precisely centered within a few ten-thousandths of an inch.

9-lb armboard
Like its platter, the Debut Mk.V's solid acrylic armboard is fitted with various-diameter brass inserts, as well as with three tiny holes for aligning with the three small metal locating pins at the bottom of the armboard well. Once the armboard has been lowered into place, there is absolutely no play. According to Conti, the pin is 0.001" smaller than the hole. The resulting fit features 0.0005" "maximum uncertainty"—ie, as good as certain—and ensures perfect, repeatable cartridge alignment when you swap armboards.

That was my experience. I removed and reinstalled the armboard many times; the overhang remained precisely locked in place.

Motor drive
The Debut Mk.V features a square-cased AC synchronous motor mounted to the top of the acrylic base with three elastomer discs sandwiched between. The motor case fits into a large square cut out of the bottom of the upper plinth, with the aluminum double-stepped pulley protruding from a small hole in the plinth.

The pulley is spec'd—to the same ±0.0005" tolerance as the platter/bearing assembly, and using the belt-riding surface to measure)—only after it's been attached to the motor shaft using a special cylindrical-fit adhesive. Conti claims the adhesive never goes "off round," while screws invariably cause uneven pulley placement on the shaft.

Drive is via a flat belt,which rides on a crowned 331/3rpm and 45rpm pulley combo. Conti and many other designers believe such a system is measurably and sonically superior to the O-ring drives found in some other 'tables—including the VPI TNT and Simon Yorke, my former and current references.

As he ran me through the Debut's technology, Conti continually stressed the difference between good design and good execution: "You can spec and design a good pulley, but if you can't execute, what's the difference?" By "execute," he meant being sure to spec the pulley roundness on the actual motor shaft used to spin it.

In its design and construction, fit'n'finish, and overall look and feel, the Debut exudes quality and design ingenuity...though I wondered whether the fixed-motor, spring-suspended plinth design, wherein any chassis movement changes the distance between the platter and the motor pulley and thus changes the belt tension, would result in the slightly edgy, sharp sound I noted when I reviewed the SOTA Cosmos 'table close to a decade ago.